Fig.REF (a) shows the schematic of the PPLN device. The top width of the fabricated ridge waveguide was \(1.8\,\mathrm {m}\)  with an etching depth of 375 \(\mathrm {nm}\)  and the length of the poled section was 6 \(\mathrm {mm}\) . The poled device is imaged with a scanning electron microscope which directly reveals the domain structures (Fig.REF b). Fig.REF (c) plots the simulated effective mode index for the fundamental and second harmonic modes along with the required poling period. The poling period is varied around \(2\,\mathrm {m}\)  which is among the shortest poling periods achieved with thin-film LN. [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}.
<FIGURE>